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Aug 30, 2023

Ship Tracks May Have Contributed to Global Cooling, Says Study

The world experienced record-breaking heat this year, with July being the hottest month in 120,000 years. While global warming due to greenhouse gas emissions is the primary cause, scientists have now

The world experienced record-breaking heat this year, with July being the hottest month in 120,000 years. While global warming due to greenhouse gas emissions is the primary cause, scientists have now discovered an unexpected factor: ship tracks.

In 2020, the International Maritime Organization (IMO) implemented a new standard requiring an 86 percent reduction in fuel sulfur content to mitigate the harmful effects of sulfur oxide emissions on human health and the environment. The reduction in sulfur emissions led to a 10 percent decrease in global emissions of sulfur dioxide.

However, an unintended consequence of the policy was a significant reduction in ship tracks. Ship tracks are aerosol clouds formed by cargo ships, which induce a brightening effect on ocean clouds due to water vapor condensation.

A NASA study analyzed satellite imagery and found that ship-track density decreased by more than 50 percent in major shipping routes after the implementation of the IMO regulation. While the decline in shipping during the COVID-19 pandemic also played a part, it was overshadowed by the impact of the sulfur regulation.

Interestingly, ship tracks have had a cooling effect on the Earth by reflecting sunlight back into the atmosphere. This cooling effect has been observed in both visible and “invisible” tracks that brightened clouds. According to Science, the increase in light caused by the IMO regulations has warmed the planet by 0.1 watts per square meter.

While the unintended consequence of ship track reduction is a cause for concern, it does provide insight into potential geo-engineering strategies to address climate change. One proposed method is marine cloud brightening, which involves injecting salt particles into the air to replicate the cooling effect of ship tracks.

The decline in ship tracks resulting from the IMO policy suggests that intentional manipulation of cloud brightness could be achieved. This finding opens up possibilities for further research and experimentation with geo-engineering techniques.